I just had this experience again with one of the obnoxious moe communities. NSFW/porn-adjacent stuff is most of what I have blocked because I don’t like it. I don’t want questionable pseudo-porn in my feed at all, and it’s really hard to avoid (though real porn was easy enough to block).
I had them all blocked, but a new one got rolled up (I assume that dude keeps rolling them up to get around the plethora of blocks those communities have) and I hadn’t encountered it yet. It shared a gross post I’d otherwise never have had the displeasure of seeing.
Perhaps a toggle setting to either block those cross posts or not, so people who are trying to block the content can, while those trying to block the places but not the content can also do that.